I always upload images to https://imgur.com/ (I think it was @bgoo who first told me about that). You don't need to create an account, you just click the 'New post' button.

Doesn't using [img] [/ img] tags on an attachment work (or is it simply not possible to use them?)?: it's been a while since I bothered with attachments.

you can do it with attachments but it's convoluted (attach the image> submit the post> click the thumbnail and right click the blown up image to get the image url > edit the post to replace the attachment with the image url in img tags. but you still have to deal with forum upload limits that way).

yeah, use imgur, @summerprincess (it's pretty intuitive to use, but if you have problems read this (you can also just drag and drop, i wrote those instructions for someone not computer literate)). you can use it without making an account, but if you wanna go back and delete it someday then you gotta make an account.